Methods are known for molding an annular lip type shaft seal of the type having an elastomeric body or seal element with a resin liner (such as of polytetrafluoroethylene) integrally molded therewith and bonded thereto. Such known method includes placing a resin washer, an elastomeric preform and metal shell in a mold and closing the mold, see for example, Japanese patent publication Sho No. 46-2381, announced July 7, 1971 in the Japanese Patent Agency Patent Gazette. Such prior art has the problem of control over the degree or uniformity of axial length to which the resin liner is formed or extruded axially beyond the molded or trimmed lip of the seal, during the molding operation. If the liner flows too far it can thin out and split and can become trapped between elastomer and the metal shell causing bond problems in critical areas, or the liner can occupy part of the flex section of the seal affecting seal performance. This problem becomes more acute with increases in the viscosity or shearing force of the elastomer and with increasing lip diameters of the seal as well as with other factors involving the characteristics of the type and thickness of the resin being used.
It is an object of the present invention to provide an improved method for controlling the resin liner flow during molding and thereby to reduce the percentage of rejects occurring during molding shaft seals having resin liners due to undesired flow of the liner during molding
It is another object of this invention to prevent liner material from entering the seal flex section.
It is another object of the present invention to provide a method for making an annular lip type shaft seal of the type having an annular elastomeric shaft seal element and a resin liner integrally molded therewith and bonded thereto, wherein the mold is provided with a step or shoulder and wherein the parameters of the angle the shoulder surface makes with the mold core, the shoulder height with respect to the liner thickness, and the initial viscosity of the elastomeric preform are maintained at certain relative values or ranges of values.